The present invention relates to flame retardant compositions which are phosphorus-containing esters, and which are particularly adapted to prevent crystallization and exuding or oiling out when these compositions are employed in organic polymers. Esters of various types have been employed as flame retardant components of various polymers. However, a common difficulty when using such esters has been the incompatibility of the ester with the organic polymer base material, for example, polyamides such as nylon, for example nylon 6,6. The additive esters have sometimes crystallized after a period of time, or have been exuded out of the polymer so that the desired flame-retardant modifying effect on the organic polymer was lost.
The present polymeric esters are ternary compounds which are formed from alcohol components and phosphorus-containing acid halides, esters or amides. The polymeric esters have at least three of the alcohol and phosphorus moieties in the product. Control of the relative proportions of the alcohol and of the phosphorus moieties as well as the relative molecular weight of the starting materials and of the final polymeric esters makes it possible to obtain products having properties of solubility, melting point and crystallization temperature to provide flame retardant properties and other physical properties without the difficulties of exuding or crystallization.